Video encoding method and apparatus, and video decoding apparatus

Abstract

To allow a finer quantization control according to the property of an image within a macroblock, quantization parameter values are allowed to be changed in units of sub-blocks equal to or smaller than the macroblock in a similar manner as in motion compensation and orthogonal transform processes. A finer-tuned quantization control is performed, for example, by selecting fine and coarse quantization parameters respectively for corresponding sub-blocks if a plurality of images having different properties coexist within the macroblock.

The invention claimed is: 
     
       1. A video encoding method for dividing each frame of a video into blocks of a predetermined size, and for encoding each of the blocks by combining temporal compression using pixel difference data and motion compensation, an orthogonal transform for transforming spatial information into frequency information, and quantization of an orthogonal transform coefficient, by using a quantization parameter defined corresponding to the blocks of the predetermined size, the video encoding method comprising:
 further dividing the blocks of the predetermined size into sub-blocks of a size smaller than the predetermined size; 
 deciding a quantization parameter for each of the sub-blocks according to an image property; 
 quantizing the orthogonal transform coefficient with the quantization parameter for each of the sub-blocks; and 
 encoding the decided quantization parameter, wherein 
 each of the sub-blocks for which the quantization parameter is decided has a size equal to or larger than a block size that is a unit of processing in the orthogonal transform, 
 when a plurality of left blocks that are adjacent to a left end of the sub-block to be encoded are present and a plurality of upper blocks that are adjacent to an upper end of the sub-block to be encoded are present as an encoded block of the predetermined size or an encoded sub-block, a difference between an intermediate value between a quantization parameter of further upper block among the left blocks and a quantization parameter of further left block among the upper blocks, and a quantization parameter the sub-block to be encoded is encoded.